Math Thread

[Friend]

ill check it out.

[electrowizard]

@Friend

data oriented design/programming

Got any resources on this?

[Friend]

not good ones i wish i did im mostly learning on my own due to lack of good resources.

i'm using unity ECS to learn it but this same concept is used in Insomniac's engine and a lot of other modern engines. (unity actually poached some of their engine programmers to write their new engine code). This blog post they did is a decent summary of the reason to use it/a higher up explanation.

ECS Data Layout

ECS groups all entities that have the exact same set of components together in memory. It calls such a set an archetype. An example of an archetype is: “Position & Velocity & Rigidbody & Collider”. ECS allocates memory in chunks of 16k. Each chunk will only contain the component data for entities of a single archetype.

Instead of having the user Update method searching for other components to operate on at runtime, per Orbit instance, in ECS land you have to statically declare “I want to run some operations on all entities that have both a Velocity and a Rigidbody and an Orbit component. To find all those entities, we simply find all archetypes that match a specific “component search query”. Each archetype has a list of Chunks where entities of that archetype are stored. We loop over all those chunks, and inside each of the chunks, we’re doing a linear loop of tightly packed memory, to read and write the component data. This linear loop that runs the same code on each entity also makes for a likely vectorization opportunity for Burst.

In many cases, this process can be trivially split up into several jobs, making the code operating the ECS component run on nearly 100% core utilization.

ECS does all this work for you, you just need to supply the code that you want to run on each entity. (You can do the chunk iteration manually if you want to though.)

When you add/remove a component from an Entity, it switches archetype. We move it from its current chunk to a chunk of the new archetype, and back swap the last entity of the previous chunk to “fill the hole”.

In ECS, you also statically declare what you intend to do with the component data. ReadOnly or ReadWrite. By promising (the promise is verified) to only read from the Position component, ECS can get more efficient scheduling of its jobs. Other jobs that also want to read from the Position component won’t have to wait.

This data layout also allows us to deal with a long-standing frustration we’ve had, which are load times and serialization performance. Loading/streaming ECS data for a big scene isn’t much more than just loading raw bytes from disk and using them as is.

This is the reason the Megacity demo loads in a few seconds on a phone.

this video is what made me decide to learn it. it has an extra clickbait title but the content is decent.

CppCon 2018: Stoyan Nikolov “OOP Is Dead, Long Live Data-oriented Design”

[Matticus]

I use linear algebra on a daily basis in game programming, but there's plenty of programmers even in games that manage to avoid it entirely. But I'd say especially in indie development it's a hard requirement. We'd all probably be better off if we understood more math.

[electrowizard]

Yeah, I'd agree they should know it anyways. It's the basis of parallel computing, so it's super important

[Friend]

i wish i tried harder in my math classes in college / retained more info.

going through the basics again has been pretty helpful and its a lot faster the second time.

[electrowizard]

@Friend

its a lot faster the second time

Yeah, that's definitely true for all math. Always makes you wonder how you were so dumb that you struggled with it before

[_jdance]

@electrowizard

i do not understand the question.

[electrowizard]

How many degrees does a triangle have? You know one angle exactly, and one in terms of x. So you can solve for the last in terms of x. I can give more info if this isn't enough help: I've got it written up already.

[electrowizard]

Ah, didn't notice x is an exterior angle. To figure out the angle BAC in terms of x, you know the angle of the entire straight line, so solve for the interior angle BAC in terms of x.

There's some property of interior/exterior angles I don't remember, but it isn't necessary, and probably comes from the result of this.

[_jdance]

How is this not possible?

A + B > C in order to form a triangle

If A = 12, B = 7, C = 4 then 12 + 7 > 4 = 19 > 4

Why doesn't this work?

[electrowizard]

Construct a triangle with those sides. Figure out what the angles would have to be

[_jdance]

cool problem

[KrazyKat]

4+7=11
11<12
Impossible.

[_jdance]

Hehe

[a2pas]

[_jdance]

[_jdance]

another cool problem

[_jdance]

[_jdance]

@electrowizard

my mind is BLANK how do i find the inverse of this